The present invention relates to an automatic transmission. In particular, it relates to technology which aims to increase the compactness of an automatic transmission comprising an input member, a plurality of planetary gearsets, three clutches, two brakes, and an output member, with at least six forward gears and reverse being attainable through appropriate engagement and disengagement of the three clutches and two brakes.
The recent trend is to make automatic transmissions which are more stepped or graduated to provide slightly more forward gear ratios that can be selected in an aim for improvement in drivability and fuel efficiency. Japanese Patent Provisional Application 2000-55152 discloses an automatic transmission where six forward speeds and reverse are selectable and employs a double-pinion type Ravigneaux compound planetary gear train which has two sets of planet-pinions, each set being meshed with a different sun gear, and will now be discussed with reference to FIG. 9. The automatic transmission disclosed therein comprises a first clutch C10 and a second clutch C20 which are selectably engageable to direct rotation that has been reduced in speed. The automatic transmission also comprises a planetary gear train G, which as has been stated is a Ravigneaux compound type, and it is common to dispose first clutch C10 and second clutch C20 behind and around planetary gear train G, and to dispose a first brake B10, in this case a band brake as shown in FIG. 9, about an outer circumference of first clutch C10 and second clutch C20, and to dispose a second brake B20 in a single row with first clutch C10 and second clutch C20.
However, according to the related art, first clutch C10, second clutch C20, and second brake B20, which is a clutch-type brake, are disposed in a row in the axial direction of the transmission assembly around an outer periphery of planetary gear train G, and this leads to a problem of the axial length of the transmission assembly being large. Also, one of the planetary gearsets constituting planetary gear train G is a double-pinion planetary gearset, and rotation having an increased torque after being reduced in speed by the reduction planetary gearset is input to planetary gear train G from a first sun gear S10 and a second sun gear S20 thereof, meaning that an outer diameter of planetary gear train G must be large, and consequently the transmission assembly becomes undesirably large overall.
It is therefore an object of the present invention to provide an automatic transmission which is more compact in both the axial and radial dimensions.